1. Field of the Invention
The present invention relates to an electromagnetic valve control system for controlling the opening and closing intake and exhaust valves which are electromagnetically actuated and also the opening and closing of an auxiliary exhaust valve associated with the exhaust valve.
2. Description of Prior Art
Intake and exhaust valves of some conventional engines are opened and closed by a camshaft. The camshaft is operatively connected to the crankshaft of the engine, so that the timing of opening and closing the intake and exhaust valves with respect to the angle of the crankshaft cannot be varied as the rotational speed of the engine varies. Since the timing of opening and closing the intake and exhaust valves is adjusted in advance to achieve a high engine efficiency at a particular engine rotational speed, the engine efficiency is lowered when the engine rotates at speeds other than the particular engine rotational speed.
Japanese Laid-Open Patent Publication No. 58(1983)-18380 discloses an internal combustion engine valve mechanism which includes a detector for detecting an operating condition of an internal combustion engine, and electric actuators for opening and closing intake and exhaust valves based on a detected signal from the detector.
Japanese Laid-Open Patent Publication No. 61(1986)-76713 also discloses an engine valve control system having an electric actuator for opening and closing an intake or exhaust valve, and a control unit for applying a pulse to the electric actuator to open the valve immediately before the valve is seated from an open position into a closed position, so that shocks imposed on the valve when it is seated are reduced.
The intake and exhaust valves themselves can be opened and closed under relatively small forces by the electric actuators such as electromagnets. When the exhaust valve is to be opened while the engine is in operation, however, a large force is required to be applied to the exhaust valve since the exhaust valve has to be moved against the pressure developed in the combustion chamber. Therefore, the electromagnet for actuating the exhaust valve is large in size, or the exhaust valve may not be opened due to the lack of a sufficient valve actuating force.
For example, if it is assumed that the pressure in the combustion chamber in the expansion stroke is 5 Kg/cm.sup.2 and the surface area of the exhaust valve which faces the combustion chamber is 8 cm.sup.2, then the electromagnetic force required to open the exhaust valve against the pressure in the combustion chamber is 40 Kg (392N). As the exhaust valve is also required to be accelerated when it is opened, the electromagnetic force of about 80 Kg (784N) must be generated by the electromagnet.
The stroke by which the intake and exhaust valves are opened and closed is difficult or impossible to change in the engines as disclosed in the above publications. Therefore, the opening and closing of the intake and exhaust valves cannot be controlled depending on the rotational speed and load of the engine, and hence do not match the actual operating condition of the engine sometimes.